Origin and Evolution of Eukaryotes – Key Vocabulary

A comprehensive set of vocabulary flashcards covering major groups, structures, and ecological roles of protists and the evolution of eukaryotes as presented in Chapter 28.

Eukaryote

Organism whose cells contain a nucleus and membrane-bound organelles.

Protist

Informal group of mostly unicellular eukaryotes that are not animals, plants, or fungi.

Endosymbiosis

Relationship in which one organism lives inside another; key process in the origin of mitochondria and plastids.

Mitochondrion

Organelle that evolved from an aerobic α-proteobacterium; site of cellular respiration.

Plastid

Photosynthetic or storage organelle (e.g., chloroplast) that descended from a cyanobacterium.

Primary Endosymbiosis

Engulfment of a cyanobacterium by a eukaryotic host, giving rise to red and green algae.

Secondary Endosymbiosis

Process in which a eukaryote engulfed a red or green alga, producing new photosynthetic lineages (e.g., euglenids, stramenopiles).

Nucleomorph

Remnant nucleus of an engulfed alga retained within some secondary plastids (e.g., chlorarachniophytes).

Excavata

Supergroup of protists with an "excavated" feeding groove; includes diplomonads, parabasalids, and euglenozoans.

Diplomonad

Anaerobic Excavata with two nuclei and mitosomes; example: Giardia intestinalis.

Mitosome

Greatly reduced, non-functional mitochondrion found in diplomonads.

Parabasalid

Anaerobic Excavata possessing hydrogenosomes; example: Trichomonas vaginalis.

Hydrogenosome

Organelle in some anaerobic protists that generates ATP and releases H₂ gas.

Euglenozoan

Excavata characterized by a crystalline rod inside each flagellum; includes kinetoplastids and euglenids.

Kinetoplastid

Euglenozoan with a single large mitochondrion containing a kinetoplast of DNA; example: Trypanosoma.

Kinetoplast

Mass of extranuclear DNA within the mitochondrion of kinetoplastids.

Euglenid

Euglenozoan with one or two flagella emerging from a pocket; many are mixotrophic (e.g., Euglena).

Mixotroph

Organism able to combine photosynthesis and heterotrophic nutrition.

SAR Supergroup

Major eukaryotic clade composed of Stramenopiles, Alveolates, and Rhizarians.

Stramenopile

Group with one "hairy" and one smooth flagellum; includes diatoms, brown algae, and oomycetes.

Diatom

Unicellular stramenopile with silica shell; major marine photosynthesizer aiding carbon cycling.

Brown Alga

Multicellular stramenopile (kelp) exhibiting alternation of generations; cell walls contain algin.

Algin

Gel-forming substance in brown-algal cell walls, useful in food and industry.

Oomycete

Water mold stramenopile with cellulose walls; many are decomposers or parasites (e.g., Phytophthora infestans).

Phytophthora infestans

Oomycete parasite that caused the Irish potato famine.

Alveolate

SAR subgroup possessing membrane-bound sacs (alveoli) under the plasma membrane.

Dinoflagellate

Alveolate with two flagella in grooves; causes red tides and can produce toxins.

Red Tide

Harmful algal bloom produced by explosive growth of some dinoflagellates.

Apicomplexan

Parasitic alveolate with an apical complex for penetrating hosts; includes Plasmodium.

Plasmodium

Apicomplexan parasite transmitted by mosquitoes, causative agent of malaria.

Ciliate

Alveolate that moves with cilia and possesses macro- and micronuclei; example: Paramecium.

Macronucleus

Large nucleus in ciliates controlling everyday functions.

Micronucleus

Smaller nucleus in ciliates involved in sexual reproduction (conjugation).

Rhizarian

SAR subgroup of mostly amoebas with threadlike pseudopodia; includes radiolarians, forams, and cercozoans.

Radiolarian

Marine rhizarian with internal silica skeleton and radial pseudopodia for prey capture.

Foraminiferan (Foram)

Rhizarian with porous calcium carbonate shell; important index fossil for paleoclimate studies.

Cercozoan

Diverse rhizarian of amoeboid or flagellated forms; some (Paulinella) possess independent chromatophores.

Chromatophore (Paulinella)

Photosynthetic organelle derived from a second primary endosymbiosis event in certain cercozoans.

Archaeplastida

Eukaryotic supergroup that includes red algae, green algae, and land plants; originated via primary endosymbiosis.

Red Alga

Mostly multicellular archaeplastid with phycoerythrin pigment; lacks flagellated gametes.

Phycoerythrin

Accessory pigment that gives red algae their color by masking chlorophyll.

Green Alga

Archaeplastid whose chloroplasts resemble those of land plants; includes chlorophytes and charophytes.

Chlorophyte

Green-algal clade containing unicellular, colonial, and multicellular species such as Volvox and Chlamydomonas.

Charophyte

Green-algal group considered the closest living relatives of land plants.

Unikonta

Supergroup comprising Amoebozoans and Opisthokonts; may have diverged earliest among eukaryotes.

Amoebozoan

Unikont with lobe- or tube-shaped pseudopodia; includes tubulinids, slime molds, and entamoebas.

Tubulinid

Free-living amoebozoan with classic "blob" morphology; heterotrophic.

Entamoeba

Parasitic amoebozoan; species E. histolytica causes amoebic dysentery.

Slime Mold

Amoebozoan exhibiting plasmodial or cellular life cycles; forms fruiting bodies under stress.

Plasmodial Slime Mold

Slime mold forming a multinucleate, single "supercell" called a plasmodium.

Cellular Slime Mold

Slime mold whose individual cells aggregate when food is scarce to form a multicellular structure.

Opisthokont

Unikont clade that includes fungi, animals, choanoflagellates, and nucleariids.

Choanoflagellate

Opisthokont protist considered the closest living relative of animals.

Nucleariid

Opisthokont amoeba closely related to fungi.

Producer (Protist)

Photosynthetic protist forming the base of aquatic food webs and fixing CO₂.

Symbiont (Protist)

Protist living in mutualistic association, e.g., dinoflagellates in coral, hypermastigotes in termites.

Parasite (Protist)

Protist that lives at the expense of a host, affecting health or ecology (e.g., Plasmodium, Pfiesteria).

Climate-Change Impact on Protists

Rising sea temperatures can reduce photosynthetic protist abundance, altering carbon cycles and food webs.